This invention relates to writing apparatus which includes an electret film as a means of receiving writing. More particularly, this invention relates to apparatus for facilitating the use of an electret film as a writing surface in presentation, display, and educational applications.
Paper has long been the predominant writing medium. However, it has suffered from certain drawbacks when used in the educational, presentation, and display fields, primarily resulting from the fact that paper is not transparent, is not easily erased and reused, and is not self-adherent.
In presentation and display applications, large pads of paper commonly known as flip charts are often affixed to an easel-like flip chart stand to hold them upright and are written upon by a speaker during the course of a presentation in order to illustrate and/or record his presentation. Such a presentation system has certain disadvantages. The paper is not easily erased and reused, and so unless the presentation is to consist merely of display of prerecorded information on successive sheets of the pad, the used sheets must be discarded after each presentation and the information written anew during the next presentation. This entails considerable expense, as well as inconvenience due to interruption of the presentation process for information to be written. It is also difficult with such flip charts to intermix preprinted information with information to be written by the speaker during the course of a presentation. Moreover, because paper is substantially opaque, the speaker cannot write new information against a background of information which was previously recorded on a separate sheet.
In order to overcome certain limitations of paper, various erasable and reusable writing media have been developed. These include chalk boards and, more recently, boards having surfaces adapted to be written upon with dry erase markers, to provide easily erasable and reusable surfaces. However, these writing media provide substantial limitations as well. They are restricted in area, and it is inconvenient to devote a portion of such area to information which is to be retained for long periods of time while other portions are erased and reused. They also do not facilitate successive writings and erasures against a background of prerecorded information.
Such drawbacks also exist in the use of paper in the educational environment. For instance, large amounts of paper are used by students in handwriting practice. Such practice and writing instruction is preferably carried out against a lined background to assist students in visualizing and controlling their writing with respect to size, spacing, and alignment of characters. While students may use paper having such a background preprinted upon it, this renders such paper unsuitable for other uses.
Others have suggested, prior to the filing date of this application, the use of plastic films which may be erasably written upon and which may adhere to a surface by "static cling". See, e.g. Canadian Patent No. 1,264,780.
It has been discovered that electret films may be erasably written upon, for instance with dry erase markers. Such electret films may be made either transparent or substantially opaque, and are self-adherent to most surfaces for extended periods of time.